Scale-Specific Viscoelastic Characterization of Hydrogels: Integrated AFM and Finite Element Modeling.

Viscoelastic hydrogels mimic the dynamic mechanical properties of native extracellular matrices, making them essential for biomedical applications. However, characterizing their scale-dependent mechanical properties remains challenging, despite their critical influence on cell-material interactions and biomaterial performance. Here, an integrated experimental-computational approach is presented to quantify and model the viscoelastic behavior of interpenetrating polymer network hydrogels across micro- and macro-scales. Atomic force microscopy-based stress relaxation tests revealed that microgels exhibit rapid, localized relaxation, while macroscopic bulk gels displayed prolonged relaxation dominated by poroelastic effects. Finite element simulations accurately replicated experimental conditions, enabling the extraction of key parameters: fully relaxed elastic modulus, relaxation modulus, and relaxation time constant. A novel analytical model is further developed to predict viscoelastic parameters from experimental data with minimal error (<6%), significantly streamlining characterization. The findings highlight the necessity of scale-specific mechanical analysis and provide a robust platform for designing biomaterials with tailored viscoelasticity for tissue engineering and regenerative medicine.